This invention relates to rocket propellants and is concerned with solid propellant charges provided with combustion inhibitors.
The arrangement of solid fuel rocket propellant charges in rocket motor cases falls into either of two classes. The first class is that of the case-bonded propellant charge in which the charge is bonded to the interior surface of a rocket motor case (i.e. body), and this bonding is frequently effected through a layer of combustion inhibition material. The second class is one in which the charge is a "grain" of solid fuel propellant which is self-supporting, and of which most of the external surface can be provided with a directly bonded layer of combustion inhibition material. The grain is then loaded into a rocket motor case and is secured therein by any convenient means. The present invention relates to the combustion inhibition material which can be used with both of the above two classes of solid fuel rocket propellant.
The principal function of the combustion inhibition material is to protect the surface of the propellant charge to which it is bonded from combustion. Thus only the areas of the propellant charge which are not coated with combustion inhibition material will combust.
A typical combustion inhibition material is cellulose acetate. This bonds well to the surface of most propellant charges, particularly the double-base propellants based on nitrocellulose and nitroglycerine which are known to those versed in the art to be of reduced smoke evolution. For such a double-base propellant charge the good bonding effect principally arises from the mutual solubility of the cellulose acetate and nitroglycerine, but although this gives a good bond, it provides a poor storage life because the cellulose acetate continually receives nitroglycerine and in time becomes highly combustible itself, thereby no longer acting to inhibit combustion.
To provide a longer storage life, it has been proposed to replace cellulose acetate by elastomeric materials which can be polymeric or non-polymeric. Suitable elastomeric materials can be bonded satisfactorily to solid propellants, and can be selected so as to be impermeable by nitroglycerine, but they suffer from the disadvantage that during combustion of the propellant at least some of the elastomer will also be combusted, and this can produce large volumes of dense smoke. The smoke has two principal disadvantages of which the first is that the flight of the rocket can be badly obscured from view to render visual guidance of the rocket difficult, and of which the second is that, conversely, the flight of the rocket is so well-marked that it can be easily observed and tracked from a distance.
It is an object of the present invention to provide a combustion inhibitor for solid fuel rocket propellants which is efficient for inhibiting combustion and which does not suffer from the disadvantage of emitting obscuring smoke when combusted.